Christina Aguilera's surprise subway performance with Jimmy Fallon

The two attempted to go incognito by covering themselves in hats, sunglasses, wigs, and unglamorous clothing, while performing Aretha Franklin's "Think." But, honestly, who were they kidding? While the costumes were pretty good, it's impossible to hide one of the greatest voices in the world, and it wasn't long before people began to realize who the undercover singers really were.

"Thank you very much. We'd like to do one more song for you if you don't mind right here. First, I'd like to introduce ourselves. My name is Jimmy Fallon," Fallon announced as he began to peel off his costume. "And this is Christina Aguilera!" The crowd that had gathered immediately began to cheer as they realized the iconic pop singer standing in front of them. And after revealing their true selves, they continued to treat their lucky audience to a performance of one of Aguilera's classic hits, "Fighter."